In particular, the present invention is an improvement on the mine seal disclosed in co-assigned U.S. Pat. No. 5,167,474 titled “Form for Making a Permanent Concrete Mine Stopping” and incorporated by reference herein for all purposes not inconsistent with this disclosure. This patent discloses a mine seal comprising two opposing spaced apart walls defined by a number of side-by-side extensible and contractible metal panels connected by horizontal ties spanning the space between the walls and by horizontal angle bars on the outside of the panels. The space between the walls is filled with full weight concrete or other suitable filler material (e.g., yieldable foamed concrete) which hardens or cures to form a permanent mine seal.
FIGS. 1-4 show four different prior art versions of a mine seal made in accordance with the invention disclosed in U.S. Pat. No. 5,167,474 which have been used commercially. In FIGS. 1A and 1B, the mine seal 1 comprises two spaced apart walls 3 made of extensible and contractible panels 5. The walls are connected by ties 9 and angle bars 15. Each tie 9 comprises a pair of end tie plates 17 connected by a metal chain 21 passing through keyhole openings 23 in the tie plates, the chain being secured in each opening by passing a link of the chain into the reduced-diameter portion of the keyhole opening 23. The tie plates 17 have V-shaped openings 27 for receiving the angle bars 15. FIGS. 2A-2C show a second variation of a mine seal 101 in which each tie 109 comprises an elongate metal plate or bar 131 having two V-shaped openings 135 adjacent opposite ends of the bar for receiving the angle bars 141. Each V-shaped opening 135 is formed by the combination of a notch 145 in a respective end of the metal bar 131 and a mating notch 147 in an end piece 151 secured by suitable fasteners 153 (e.g., rivets) to the bar. FIGS. 3A-3C show a third variation of a mine seal 201 in which each tie 209 comprises an adjustable-length elongate metal plate or bar 231 made of multiple overlapping sections 233 secured together by suitable fasteners 235 (e.g., nut-and-bolt fasteners) extending through selected aligned holes 236 in the overlapping sections. The bar 231 has two V-shaped openings 237 adjacent opposite ends of the bar for receiving the angle bars 239. Each V-shaped opening 237 is formed by the combination of a notch 245 in a respective end of the metal bar 231 and a mating notch 247 in an end piece 251 secured by suitable fasteners 253 (e.g., rivets) to the bar. FIGS. 4A-4B show a fourth variation of a mine seal 301 in which each tie 309 comprises a pair of end tie plates 341 connected by a metal rod 343 secured to the end tie plates. The end tie plates 341 have V-shaped openings 353 for receiving the angle bars 355.
In the various embodiments of the above-referenced mine seal, the ties 9, 109, 209 and 309 are of a conductive material. Recently, MSHA (Mine Safety and Health Administration of the U.S. Department of Labor) has promulgated rules prohibiting conductors through permanent seals.